Chapter 097. Paraneoplastic Neurologic Syndromes (Part 4) PND of the Central Nervous System and Dorsal Root Ganglia When symptoms involve brain, spinal cord, or dorsal root ganglia, the suspicion of PND is usually based on a combination of clinical, radiologic, and CSF findings. In these cases, a biopsy of the affected tissue is often difficult to obtain, and although useful to rule out other disorders (e.g., metastasis, infection), neuropathologic findings are not specific for PND. Furthermore, there are no specific radiologic or electrophysiologic tests that are diagnostic of PND. The presence of antineuronal antibodies (Table 97-2) may help in the diagnosis with the following caveats: (1) antibodies are detected in only 60–70% of PNDs of the CNS; (2) antibodies may be present in both the serum and CSF, but in some patients only the CSF is positive (especially with antibodies to Tr and Ma proteins); (3) antibodies (usually at low titer) are present in a variable proportion of cancer patients without PND; (4) there is an imperfect correlation between antibody titers and the course of the neurologic disorder; (5) several antibodies may associate with a similar syndrome, with the antibody specificity often correlating with the tumor type (e.g., cerebellar degeneration is associated with anti-Tr antibodies if the tumor is Hodgkin's disease but with anti-Yo antibodies if the tumor is ovarian or breast cancer); and (6) several antibodies may be present in the serum or CSF of the same patient (e.g., anti-Hu and anti-CV 2 /CRMP5). MRI and CSF studies are important to rule out neurologic complications due to the direct spread of cancer, particularly metastatic and leptomeningeal disease. In most PNDs the MRI findings are nonspecific. Paraneoplastic limbic encephalitis is usually associated with characteristic MRI abnormalities in the mesial temporal lobes (see below), but similar findings can occur with other disorders [e.g., nonparaneoplastic limbic encephalitis with antibodies to VGKC, human herpesvirus (HHV) 6 encephalitis] (Fig. 97-2). The CSF profile of patients with PND of the CNS or dorsal root ganglia typically consists of mild to moderate pleocytosis (<200 mononuclear cells, predominantly lymphocytes), an increase in the protein concentration, intrathecal synthesis of IgG, and a variable presence of oligoclonal bands. Figure 97-2 Fluid- attenuated inversion recovery sequence MRI of a patient with limbic encephalitis and voltage- gated potassium channel antibodies. Note the abnormal hyperintensity involving the medial aspect of the temporal lobes. PND of Nerve and Muscle If symptoms involve peripheral nerve, neuromuscular junction, or muscle, the diagnosis of a specific PND is usually established on clinical, electrophysiologic, and pathologic grounds. The clinical history, accompanying symptoms (e.g., anorexia, weight loss), and type of syndrome dictate the studies and degree of effort needed to demonstrate a neoplasm. For example, the frequent association of LEMS with SCLC should lead to a chest and abdomen CT or body positron emission tomography (PET) scan and, if negative, periodic tumor screening for at least 3 years after the neurologic diagnosis. In contrast, the weak association of polymyositis with cancer calls into question the need for repeated cancer screenings in this situation. Serum and urine immunofixation studies should be considered in patients with peripheral neuropathy of unknown cause; detection of a monoclonal gammopathy suggests the need for additional studies to uncover a B cell or plasma cell malignancy. In paraneoplastic neuropathies, diagnostically useful antineuronal antibodies are limited to anti-CV 2 /CRMP5 and anti-Hu. For any type of PND, if antineuronal antibodies are negative, the diagnosis relies on the demonstration of cancer and the exclusion of other cancer-related or independent neurologic disorders. Body PET scans often uncover tumors undetected by other tests. . Chapter 097. Paraneoplastic Neurologic Syndromes (Part 4) PND of the Central Nervous System and Dorsal Root Ganglia When. variable proportion of cancer patients without PND; (4) there is an imperfect correlation between antibody titers and the course of the neurologic disorder; (5) several antibodies may associate. important to rule out neurologic complications due to the direct spread of cancer, particularly metastatic and leptomeningeal disease. In most PNDs the MRI findings are nonspecific. Paraneoplastic